摘要
针对传统室温熔盐价格昂贵、粘度大、电化学稳定性差等缺点,将Li NO_(3)引入高沸点有机溶剂1,3-二甲基-2-咪唑啉(DMI)中制备了一种新型阳离子溶剂化型室温熔盐([Li(DMI)_(n)]^(+)[NO_(3)]^(-))体系,具有电化学稳定性高、价格低廉等优点。研究了以上游廉价Sm Cl3为原料从该新型溶剂化介质电沉积稀土金属钐(Sm)过程的若干物理化学问题。^(7)Li核磁共振(NMR)技术证实Li+是以溶剂化阳离子([Li(DMI)n]+)形式存在,二元DMI-Li NO_(3)体系可视作溶剂化介质。采用循环伏安(CV)技术研究了电沉积金属钐过程的电极反应机制,金属Sm的沉积是两步得电子还原过程;通过恒电位法制备了稀土金属Sm并通过扫描电镜-能谱(SEM-EDS)和X射线光电子能谱(XPS)技术对沉积镀层进行了形貌和元素分析。提出一种溶剂冶金新技术路线,可为低碳、低成本常温电化学提取大块稀土金属及其中间合金提供科学依据和应用基础。
The development of green extraction metallurgy and recycling technology of rare earth metals is of great significance and strategic value to accelerate the breakthrough of key common technologies in the field of rare earth functional materials.The industrial production of rare-earth metals is often achieved by molten salt electrolysis or vacuum thermal reduction,which has the disadvantages of high energy consumption,long process and complex operation.Ionic liquid is a room temperature molten salt with unique physical and chemical properties,providing new ideas for the low-temperature electrochemical and efficient preparation of rare earth metals.Therefore,it has attracted extensive attention in the field of rare earth metals electrowinning.However,at present,the synthesis pro⁃cess of ionic liquids is complex and the cost is high,and the synthesized ionic liquids have disadvantages such as strong water sensitiv⁃ity,high viscosity and poor solubility,which seriously restrict the large-scale process in the electrodeposition of rare earth metals.Therefore,the development of a new functional electrolyte system with low cost,practicality and excellent physicochemical properties(such as high chemical solubility,high stability,low viscosity,high boiling point,etc.)has important scientific significance and ap⁃plication value for green,economic and efficient electrochemical extraction,separation or recovery of rare earth metals.In this study,a cationic solvate room temperature molten salt or Li-containing solvate ionic liquid([Li(DMI)_(n)]^(+)[NO_(3)]^(-))electrolyte system prepared by adding a certain amount of LiNO_(3) into the organic molecular liquid 1,3-dimethyl-2-imidazolinone(DMI),was proposed and ap⁃plied to the electrochemical extraction of metallic samarium at room temperature with SmCl3 as raw material.^(7)Li nuclear magnetic reso⁃nance(NMR)technology confirmed that Li^(+)existed in the form of solvated cation,and the binary DMI-LiNO_(3) system could be regard⁃ed as solvation medium.DMI was a highly polar functional aprotic solvent with high boiling point and excellent salt solubility,and had the background of industrial synthesis.Therefore,compared with the traditional first/second generation and reported special ionic liq⁃uids,it had more metallurgical application prospects.The electrochemical behavior and deposition mechanism of Sm(III)in this new solvation medium were explored by cyclic voltammetry(CV)technology.CV and potentiostatic experimental results showed that the bi⁃nary DMI-SmCl3 system could not be used for Sm electrodeposition.This was because rare earth elements had a relatively complex coor⁃dination environment,and DMI could form a highly stable complex with Sm(III),which made it impossible to electrodeposit metallic Sm.However,CV results showed that it was possible to electrodeposit Sm in this electrolyte system under the support of LiNO_(3).The re⁃duction of samarium was a two-step electron reduction reaction including Sm(III)+e-→Sm(II)and Sm(II)+2e-→Sm(0).The oxida⁃tion signals of Sm were also observed in CV curves from the ternary DMI-SmCl_(3)-LiNO_(3) system.It was considered that LiNO_(3) played a key role in the electrochemical performance of Sm electrodeposition in such electrolyte system.Nitrate anions could destroy the strong coordination complex formed between Sm(III)and DMI to some extent,resulting in electroactive species which easily discharged.The observed electrochemical reduction signals could be preliminarily attributed to the mutual exclusion of Lewis acidic NO_(3)^(-)and sol⁃vate Lewis acidic Sm-containing ionized species.Furthermore,the addition of Li+could increase the conductivity of the overall electro⁃lyte and reduce the solvation number of Sm(III).Therefore,it was conducive to the electrodeposition of metallic Sm.The metals ob⁃tained by potentiation deposition(-2.5 V(vs.Ag/Ag^(+)))on high purity Al substrate during 30 min were characterized and evaluated by high resolution X-ray photoelectron spectroscopy(XPS)and scanning electron microscope(SEM)combined with energy dispersive spectroscopy(EDS).XPS confirmed that the deposit contained Sm in the form of metals and oxides and the presence of Sm^(2+)was not found.SEM with different magnification also showed that the metallic Sm was spherical particles with partial oxidation.In the selected area,the content of samarium element determined by EDS was up to 72.25%(mass fraction).In addition to Al element energy spec⁃trum signal caused by Al substrate,it was found that there was a content of 7.93%(mass fraction)belonging to oxygen signal.This was because the oxidation of the sample in contact with the air during the inspection process and entering the instrument test bench,show⁃ing the difficulty and complexity of electrodeposition of active metals at room temperature.Finally,a short process for the preparation of rare earth metals and their alloys by room temperature electrochemical solve metallurgy-heat treatment was proposed.Compared with the preparation of rare earth metals by molten salt electrolysis and thermal reduction,the technical path proposed in this study had ob⁃vious advantages.To summarize,this study could provide scientific and application basis for low-carbon and low-cost electrochemical extraction of rare earth metals at the lowest possible temperature.
作者
王立
张保国
张维民
刘风国
张丽鹏
石忠宁
Wang Li;Zhang Baoguo;Zhang Weimin;Liu Fengguo;Zhang Lipeng;Shi Zhongning(School of Chemistry and Chemical Engineering,Shandong University of Technology,Zibo 255049,China;School of Metallurgy,Northeastern University,Shenyang 110819,China)
出处
《稀有金属》
EI
CAS
CSCD
北大核心
2023年第4期594-600,共7页
Chinese Journal of Rare Metals
基金
国家自然科学基金项目(51574160,21776175,51804070)
先进耐火材料国家重点实验室开放基金项目(SKLAR202007)资助。
关键词
金属钐(Sm)
熔盐电解
稀土金属
溶剂化介质
溶剂冶金
metallic samarium(Sm)
molten salt electrolysis
rare earth metals
solvate medium
solvemetallurgy
